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Gradients in compositions in the starchy endosperm of wheat have implications for milling and processing
Background: Wheat is the major food grain consumed in temperate countries. Most wheat is consumed after
milling to produce white flour, which corresponds to the endosperm storage tissue of the grain. Because the
starchy endosperm accounts for about 80% of the grain dry weight, the miller aims to achieve flour yields
approaching this value.
Scope and approach: Bioimaging can be combined with biochemical analysis of fractions produced by sequential
pearling of whole grains to determine the distributions of components within the endosperm tissue.
Key findings and conclusions: This reveals that endosperm is not homogeneous, but exhibits gradients in composition
from the outer to the inner part. These include gradients in both amount and composition. For example,
the content of gluten proteins decreases but the proportion of glutenin polymers increases from the outside to the
centre of the tissue. However, the content of starch increases with changes in the granule size distribution, the
proportions of amylose and amylopectin, and their thermal properties. Hence these parts of the endosperm differ
in the functional properties for food processing. Gradients also exist in minor components which may affect
health and processing, such as dietary fibre and lipids. The gradients in grain composition are reflected in
differences in the compositions of the mill streams which are combined to give white flour (which may number
over 20). These differences could therefore be exploited by millers and food processors to develop flours with
compositions and properties for specific end uses